This invention relates to a device and method for producing single-crystal ingot (particularly silicon single-crystal ingots) by the Czochralski method (CZ method).
The method for pulling single-crystals by the CZ method is commonly known art, and CZ method devices for producing single-crystal ingot are in wide use. In obtaining a single-crystal by the CZ method, the single-crystal is pulled up from the liquid surface of the raw material. The pulling speed and other conditions are variously set so as to reduce crystal defects and the like in the single-crystal that is pulled. What is being done more recently includes performing rapid cooling through the temperature region of defect formation, thereby diminishing the size of crystal defect, and making the wafer surface layer a defectless layer in subsequent heat treatment. By performing rapid cooling, the efficiency of producing single-crystal ingots can be enhanced.
As to performing the rapid cooling of single-crystals being pulled, there is a technology in which a cooler is disposed in the CZ furnace (WO93/00462 publication (Japanese Patent No. 2,562,245)). As is indicated in that publication, for the coolers used to perform the rapid cooling, cooling pipelines through which cooling water flows are generally adopted in the interest of ease of use and general purpose characteristics of the construction.
However, when a cooling pipeline through which cooling water flows is used as a cooler, there is a problem in that enormous damage will be inflicted on the device if and when the cooling pipeline fails and cooling water leaks out. When such an accident as this occurs, not only is the single-crystal ingot pulling environment adversely affected, but sometimes such an accident will lead to a situation wherein the production process is stopped, and the stable supply of single-crystal ingots is impeded.
In view of such problems as noted above, an object of the present invention is to effect improvements, in a single-crystal ingot producing device equipped with a cooler comprising a pipeline system through which cooling water is made to flow, to reduce device malfunctions caused by water leakage, and, simultaneously, to implement conditions for achieving maximum production efficiency.
As a result of assiduous research conducted by the inventors with a view to the problems noted in the foregoing, it was discovered that the cooler used to control crystal defects in single-crystal ingots being pulled need not be disposed in an extensive region inside the furnace, but need only be disposed in a limited narrow region. At the same time, it was confirmed that, by appropriately setting the cooling water flow volume and flow speed and the pipe diameter, etc., even when a cooler is disposed in such a limited narrow region, such a cooler functions adequately well as a cooler for raising the single-crystal ingot pulling speed and enhancing production efficiency, which leads to the completion of the present invention.
More specifically, the present invention provides the following device and method.
[Czochralski method silicon single-crystal ingot producing device]
First, the present invention provides Czochralski method silicon single-crystal ingot producing devices such as described below.
(1) A Czochralski method (hereinafter xe2x80x9cCZ methodxe2x80x9d) single-crystal ingot producing device for pulling, inside a furnace, single-crystal ingots from a raw material melt in a crucible, comprising a thermal shielding element that encloses a single-crystal ingot being pulled (hereinafter xe2x80x9cbeing-pulled single-crystal ingotxe2x80x9d) and blocks radiant heat from liquid surface of the melt; and a cooler, disposed on inside of the thermal shielding element, for cooling a prescribed portion of the being-pulled single-crystal ingot, the thermal shielding element and the cooler being provided inside the furnace, wherein the cooler comprises a cooling pipeline through which cooling water flows, and is disposed in a portion of inside of the thermal shielding element.
(2) The CZ method single-crystal ingot producing device as described above, wherein the cooler is a cooling pipeline through which cooling water flows, and encloses the being-pulled single-crystal ingot; and inner diameter of the cooler is larger than inner diameter of the thermal shielding element.
(3) The CZ method single-crystal ingot producing device as described above, wherein lower end of the cooling pipeline is positioned at a position 150 mm or less from liquid surface of the melt.
(4) The CZ method single-crystal ingot producing device as described above, further comprising at least one of detection means noted below, either singly or in combination:
{circle around (1)} a temperature sensor provided inside a gas exhaust pathway of a CZ furnace;
{circle around (2)} tracking means for tracking intake volume of a pump for exhausting gas inside the CZ furnace; and
{circle around (3)} an infrared absorbance measuring sensor provided inside the CZ furnace or inside the exhaust path of the CZ furnace.
(5) The CZ method single-crystal ingot producing device as described above, further comprising magnetic field application means for applying a magnetic field into a raw material melt inside the crucible.
(6) The CZ method single-crystal ingot producing device as described above, wherein the magnetic field application means are magnetic field application means for generating an isometrically symmetrical and radially formed cusp magnetic field inside the raw material melt.
[Pipeline Setting Method for CZ Method Single-crystal Ingot Producing Device]
(7) A method for setting a pipeline for a CZ method single-crystal ingot producing device for causing a cooling fluid to flow through a pipeline in a CZ furnace so as to rapidly cool a single-crystal ingot being pulled, wherein position of a lower end of the pipeline through which the cooling fluid flows is set low and inner diameter of the pipeline is made small, and flow speed of the cooling fluid is controlled in accordance with diameter of the being-pulled single-crystal ingot, whereby temperature gradient of the being-pulled single-crystal ingot in pulling direction is increased, device stability is enhanced, and flexibility for arranging the pipeline is enhanced.
(8) The method as describe above, wherein the pipeline used for the rapid cooling is disposed in a portion on the inside of the heat shield in the furnace.
Here, when the inner diameter of the cooling pipeline is small, even if it should happen that a water leak occurs, the volume of leaking water will be small compared to the case of a large inner diameter. Furthermore, it was confirmed by the inventors that, in that portion that is 150 mm or less (and particularly the portion that is 100 mm or less) from the liquid surface of the silicon melt, if the inner diameter of the cooling pipeline is made smaller, there is no great change in the cooling effect contributing to the temperature gradient in the pulling direction. Accordingly, making the inner diameter of the cooling pipeline smaller in that portion means that device malfunctions caused by water leakage can be reduced while maintaining the cooling effect for contributing to the control of the temperature gradient in the pulling direction. This also, at the same time, leads to the realization of improvements in production efficiency by upping the pulling speed.
According to the present invention, the flexibility the pipeline can be enhanced. This is because, if the pipeline is narrow, the accommodation volume capacity of the pipeline may be made smaller, and bending and other processing are made easier. What is significant in the present invention, however, is that the flexibility in the arrangement of the pipeline can be enhanced without diminishing the cooling effect, and in a condition of enhanced safety. That significance is particularly great when the pipeline is disposed in a portion on the inside of the thermal shielding element.
[Temperature Gradient Controlling Method for Being-pulled Single-crystal Ingot]
The cooler according to the present invention cools prescribed locations in a focused manner in order to make the temperature gradient in the direction the single-crystal ingot is being pulled larger. Therefore, the present invention also includes a method such as the following as another aspect thereof.
(9) A method for controlling temperature gradient in a pulling direction of a single-crystal ingot being pulled, the method being applied to a CZ method single-crystal ingot producing device that comprises, inside a furnace, a thermal shielding element that encloses the single-crystal ingot being pulled inside the furnace and blocks radiant heat from liquid surface of a melt; and a cooler, disposed on the inside of the thermal shielding element, that cools a prescribed portion of the being-pulled single-crystal ingot, wherein the cooler is disposed in a portion inside the thermal shielding element, whereby temperature gradient of the being-pulled single-crystal ingot in the direction of pulling is controlled.
[Other Aspects of CZ Method Single-crystal Ingot Producing Device]
The present invention further provides such CZ method single-crystal ingot producing methods as those described below.
(10) The CZ method single-crystal ingot producing device as described in any one of (1) to (6) above, wherein treatment for enhancing heat absorbing properties is carried out on surface of the cooler facing the being-pulled single-crystal ingot.
(11) The CZ method single-crystal ingot producing device as described in (10) above, wherein the treatment for enhancing heat absorbing properties includes black coloring.
(12) The CZ method single-crystal ingot producing device as described in (11) above, wherein the treatment of black coloring is performed by PVD method.
As a preferable PVD method, there is the ion plating, and as a preferable substance for configuring a film, there is titanium aluminum nitride.
If a cooler is employed that has been subjected to a surface process to enhance the heat absorbing properties, the cooling effect produced by the present invention can be enhanced even further. And, by enhancing the cooling effect, it becomes possible to make the cooler smaller.
[Another Aspect of the Temperature Gradient Controlling Method for Being-pulled Single-crystal Ingot]
The present invention, furthermore, includes a method such as the following wherein a cooler is used that has been subjected to a surface process to enhance the heat absorbing properties.
(13) The method as described in (9) above, wherein a cooler whose surface facing the being-pulled single-crystal ingot is treated so as to enhance heat absorbing properties thereof, is employed as the cooler, whereby temperature. gradient of the being-pulled single-crystal ingot in direction of pulling is controlled while enhancing heat absorbing effect generated by the cooler.
[Definition of Terms, etc.]
In this device, it is noted that xe2x80x9cthe lower end of the cooling pipeline . . . is positioned at a position 150 mm or less from the liquid surface of the melt.xe2x80x9d The upper limit of the lower end of the cooling pipeline is a position that is 150 mm from the liquid surface of the melt, but the lower limit of the lower end of the cooling pipeline is a distance wherewith the liquid surface of the silicon melt is not contacted, and should be a distance wherewith no anomalies or the like occur in the cooler due to the radiant heat from the liquid surface of the melt.
The xe2x80x9ctracking meansxe2x80x9d that track the intake volume of the pump that exhausts the gas from inside the CZ furnace may be either means such as a flow volume sensor that tracks the pump intake volume and detects changes therein that are provided separately, or means such that the pump itself in some form or other comprises such a detection mechanism. That is, in the case where the pump is, itself, subjected to inverter control, for example, changes in the intake volume appear as changes in electric power consumption, but, for the xe2x80x9ctracking meansxe2x80x9d noted earlier, cases are also included where the pump itself ascertains those power consumption changes.
With respect to the terminology xe2x80x9ceither singly or in combination,xe2x80x9d by xe2x80x9csinglyxe2x80x9d is meant the adoption of any one of items {circle around (1)}, {circle around (2)} and {circle around (3)} above, while xe2x80x9cin combinationxe2x80x9d means a combination of two or more different items, such as {circle around (1)} and {circle around (2)}, or {circle around (1)} and {circle around (3)}, or {circle around (1)}, {circle around (2)} and {circle around (3)}. By xe2x80x9cat least one, respectively,xe2x80x9d is meant that combinations of two or more of the same type are allowed, such as the combination of {circle around (1)} and {circle around (1)} in the single case of {circle around (1)}, or {circle around (1)} and {circle around (1)} and {circle around (2)} in the case of a combination of {circle around (1)} and {circle around (2)}. In other words, the adoption of such a form as two temperature sensors and one flow volume sensor is also included in the concept of this device.
By xe2x80x9ctemperature sensorxe2x80x9d is meant something like a thermocouple, for example. By xe2x80x9cflow volume sensor,xe2x80x9d moreover, is meant something that, in some fashion or other, measures the flow volume of a gas, which includes both things that measure the volume of gas passage and things that directly measure the speed of gas passage. The xe2x80x9cinfrared absorbance measuring sensorxe2x80x9d may be either something that measures the volume of infrared radiation absorbed or something that measures the absorption rate. Nor does it matter whether the xe2x80x9cinfrared absorbance measuring sensorxe2x80x9d is a reflecting type or a transmitting type.
For the xe2x80x9cmagnetic field application means for applying a magnetic field inside the raw material melt inside the cruciblexe2x80x9d, something like that disclosed in Japanese Patent Application Laid-Open No. 56-45889, for example, can be used. And for the xe2x80x9cmagnetic field application means for producing . . . a cusp magnetic field,xe2x80x9d something like that disclosed in Japanese Patent Application Laid-Open No. 58-217493 can be used.
The xe2x80x9ccooling fluidxe2x80x9d typically is water. However, there is no limitation on the type in this method so long as it is a fluid that conveys heat efficiently, and a gas or liquid other than water can also be used.
Examples of a xe2x80x9cprocess with which the heat absorbing properties are enhancedxe2x80x9d include not only processes that include a xe2x80x9cblack film formation. process (i.e. coloring process)xe2x80x9d like that described subsequently in an embodiment, but, even in a coloring process, the color need not be black if it is a color that will cause the infrared radiation reflectivity to be reduced (a process for coloring brown or dark red or the like, for example). Also included, in addition to coloring processes other than black coloring, are processes that change the shape or surface of the cooler and thus cause the thermal reflectivity to be reduced, for example (such as a process or the like that forms irregularities on the surface, for example).
With respect to the terminology xe2x80x9cprocess that includes a black coloring process,xe2x80x9d the term xe2x80x9cincludesxe2x80x9d means that a process other than a xe2x80x9cblack coloring processxe2x80x9d may be included in the xe2x80x9cprocess wherewith the heat absorbing properties are enhanced.xe2x80x9d Accordingly, for example, together with the xe2x80x9cblack coloring processxe2x80x9d noted earlier, processing that includes a coloring process other than that black color process, and processes that change the shape or surface of the cooler and thus cause the thermal reflectivity to be reduced, for example (such as a process that forms irregularities on the surface) may also be used.
In addition to the sputtering and ion plating adopted in embodiments described subsequently, the xe2x80x9cPVD methodsxe2x80x9d also include vapor deposition. Nevertheless, it is preferable that ion plating be used due to the tight bonding. properties of the films formed. The use of sputtering is also preferable in cases where variety in the elements configuring the film is taken into consideration.
In the method and device according to the present invention, there are no factors that are influenced by the type of the single-crystal ingot that is pulled, and the method is considered to be a method that can be applied to CZ methods in general. Therefore, single-crystal ingots being pulled are not limited to silicon single-crystal ingots.